The Solar System – ASTR 121

First Midterm – April 20, 2015, 11:00-11:50

Instructions:  Print your name and student identification number at the top of this page.  Answer each of the questions A through J in the space provided.  Be clear and thorough in your answers using sentences, labeled diagrams, and formulas with symbols defined, where appropriate.  Each question is worth two points.

A.  Define an Astronomical Unit (AU).

B.  What is the ecliptic plane?

C.  What is a solstice?

D.  What is stellar parallax?

E.  Why do we always see the same face of the Moon?

F.  State Kepler's second law of planetary motion, explaining any technical terms you use.

G.  What do we mean by the Ptolemaic model of the universe?

H.  Why does free fall make you weightless?

I.  State Newton’s law of universal gravitation.

J.  The Moon is about 3,000 km in diameter and has an angular size of about half a degree.  Use this data to calculate its distance from the Earth.